The flame retarders for resin, used in these years for conferring flame retardant properties on a resin composition, may be exemplified by metal hydroxide based (e.g. magnesium hydroxide or aluminum hydroxide) flame retarders, silicon based (e.g. silicone or silica) flame retarders, halogen-based (bromine) flame retarders and phosphorus-based (e.g. phosphate or red phosphorus) flame retarders.
The metal hydroxide based flame retarders suffer from the defect that they are added in larger quantities in the resin and hence the mechanical properties of the resin are impaired. The silicon-based flame retarders suffer from the defect that the sorts of the resin compositions, the silicon-based flame retarders may be applied to, are limited. On the other hand, the consumption of halogen-based flame retarders tends to be decreased because they are detected in animals or in woman's milk, or there is fear of generation of bromine-based dioxin on combustion.
Thus, the phosphorus-based flame retarders are currently attracting attention as a substitute material for the above flame retarders. However, the phosphorus-based flame retarders suffer from a problem that gases may be evolved on injection molding a resin composition, or the resin composition may be lowered in thermal resistance.
In connection with use of the polycarbonate resin, as a resin composition, a flame retarder for resin of a polystyrene sulfonate resin type, which is a metal salt flame retarder, has been proposed in JP Laid-Open Patent Publications 2001-181342, 2001-181444 and 2001-2941.
The flame retarders for resins, proposed in these Patent publications, suffer from the problem that the resin compositions, the flame retarders may be applied to, are limited to polycarbonate resins, that the flame retardant effect is insufficient, and that the flame retarders are not dispersed substantially uniformly, that is, that the flame retarders are poor in compatibility. For this reason, there is raised a demand for a flame retarder for resin exhibiting higher flame retardant properties.
In particular, a flame retarder for resin, proposed in JP Laid-Open Patent Publication 2002-2941, contains an amide group or a carboxyl group, liable to take up the moisture, such that, when the resin composition, containing the flame retarder, is stored for prolonged time, there is raised such a problem that the resin composition is discolored and impaired in appearance, or the resin itself becomes embrittled, that is, the resin is lowered in mechanical strength.